The "autobahn" is not a single road, but a series of highways, sort of like our "400 series" highways. They have instituted speed limits in a lot of areas, especially highly populated areas. I THINK there are still some areas that are unlimited.

I drove on the Autobahn back in 1982. I remember my first time, I had only been on a few minutes, and a cop merged onto the road from the right. Instinctively, I got off the gas and tried to slow down so he wouldn't "catch" me speeding.....and then I remembered it was legal, so right back on the gas. I had a 5 cylinder Audi back then that would do 220, but it didn't feel stable in the curves, so I slowed down to 180 for the curves.